A MIMO (Multiple-Input Multiple-Output) wireless system can obtain diversity and array gains by using a transmit BF (Beam Forming) or precoding technology and a receive signal combination technology. A system that uses BF or precoding may generally be expressed as:y=HVs+n, where
y represents a vector of a received signal, H represents a channel matrix, V represents a precoding matrix, s represents a vector of a transmitted symbol, and n represents a measurement noise. Optimal precoding generally requires that a transmitter completely know CSI (Channel State Information). A commonly used method is that user equipment quantizes instantaneous CSI and feeds back the CSI to a base station. CSI information that is fed back by an existing LTE R8 system includes an RI (Rank Indicator), a PMI (Precoding Matrix Indicator), a CQI (Channel Quality Indicator), and the like, where the RI and the PMI respectively indicate a quantity of used layers, and a precoding matrix. A set of used precoding matrices is generally referred to as a codebook (where sometimes, each precoding matrix therein is referred to as a codeword). A 4-antenna codebook of the existing LTE (Long Term Evolution) R8 is designed based on Householder transformation, and in an LTE R10 system, a design of dual codebooks is further introduced for an 8-antenna codebook. The foregoing two codebooks are mainly used for a design of an antenna of a conventional base station. A vertical antenna beam direction is controlled by the conventional base station by using a fixed downtilt or a remote and electrically adjusted downtilt, and the beam direction thereof can be dynamically adjusted by precoding or beam forming only in a horizontal direction.
To reduce system costs and meet requirements for higher system capacity and coverage, AASs (Active Antenna Systems) are widely deployed in practice, and enhancement of communication performance after an AAS system is introduced is considered in a currently launched LTE R12 standard. Compared with a traditional base station antenna, the AAS further provides a degree of freedom in a design in the vertical direction. The introduction of the degree of freedom in the vertical direction may be used for cell splitting, or may be used for implementing three-dimensional beam forming (3D-BF). The foregoing technologies propose new requirements in air interface aspects such as signaling support, codebook design, and feedback support. In such a background, on how to acquire cell splitting gains and improve system throughput performance by using codebook and feedback design, a new design scheme needs to be proposed.